FIG. 5 is a schematic view of background art for a system for cooling a printed circuit board. FIG. 6 is an enlarged view of a component A of FIG. 5. ICs 2 are mounted on a printed circuit board 1 which is supported between a pair of rails 3 which are arranged in parallel. Cooling pipes 4 which are branched from a header pipe 4b are arranged on an upper face of the printed circuit board 1. Cooling pipes 5 are arranged on a bottom face of the printed circuit board 1. Each cooling pipe 5 is connected to the cooling pipe 4 by a flexible tube 6, a joint pipe 7 and an another flexible tube 6. The flexible tube 6 is made of urethane resin. The cooling pipes 5 are connected to a confluence pipe 5b. A coolant supplied from an origin 8 flows to the header pipe 4b through a flexible tube 4a which is connected to the header pipe 4b by a joint 9. The confluence pipe 5b is connected to a flexible tube 5a by a joint 9.
As shown in FIG. 6 and FIG. 8, the IC 2 is fixed to the cooling pipe 4 by a J shaped elastic member 11 and a plate 12. A first end portion 11a of the elastic member 11 surrounds the cooling pipe 4 and is joined with a central portion 11b of the elastic member 11 by screws 16 in order to tightly catch the cooling pipe 4 between the first end portion 11a and the central portion 11b. Grease 14 which has a good bet conductivity is sandwiched between the elastic member 11 and the cooling pipe 4. A spacer 15 is arranged between the first end portion 11a and the central portion 11b. Screws 17 fix a second end portion 11c to the plate 12 which is bonded to an upper surface of the IC 2 by a bonding agent 18 which has a good conductivity. Grease 14 which has good heat conductivity is sandwiched between the second end portion 11c and the plate 12.
Heat of the IC 2 is transferred to the coolant, which is supplied from the origin 8 and flows in the cooling pipes 4 and 5, via the bonding agent 18, the plate 12, the grease 14, the elastic member 11 and the grease 14.
In the case of repairing the IC 2, an operator screws off the screws 17 in separate to detach the IC 2 and also screws off the screws 16 in order to depart the first end portion 11a from the central portion 11b of the elastic member 11. As shown in FIG. 7, the operator turns the elastic member 11 around an axis Ax of the cooling pipe 4 in order to separate the second end 11c from the IC 2. Then the lead wires 19, which are hidden by the cooling pipe 4 and elastic member 11, of the IC 2 are exposed to the operator, therefore the operator can easily check the leads 19 and also can check the IC 2 by using the leads 19 as terminals to which a checker which detects the characteristics of the IC 2 is touched. And the operator can also replace a failed IC with a new IC with ease.
Because the coolant flows through the header pipe 4b, the cooling pipes 4, the cooling pipes 5 and the confluence pipe 5b due to the pressure of the coolant which varies with the direction of flow of the coolant, the cooling capacity for one printed circuit board which is vertically arranged differs from the cooling capacity for another printed circuit board which is horizontally arranged. The coolant flowing through the header pipe 4b is distributed into the cooling pipes 4 and flowing resistancy of one cooling pipe 4 is not the same as another cooling pipe 4, therefore, the cooling capacity of one cooling pipe is not same as other cooling pipes.
Because the lengths of the leads 19, thicknesses of the ICs 2 and conditions of bonding between the printed circuit board 1 and the leads 19 are irregular, the distance between an upper surface of a printed circuit board 1 and an upper surface IC 2 varies. Therefore, the bottom surface of the plate 12 is not level with the upper surface of the IC 2 as shown in FIG. 8 and the heat conducting rate is low in a portion where the distance is large. Because an area of a cross section of the elastic plate 12 is not sufficient, the conductance of the heat of the conducting line from the IC 2 to the cooling pipe 4 through the plate 12 and the elastic plate 11 is high and the efficiency for cooling is not sufficient.
The elastic member 11 is attached to the cooling pipe 4 by following processes.
(i) As shown in FIG. 9, elastically bend the elastic plate 11 in order to separate the inner surface of the first end portion 11a from the inner surface of the central portion 11b. PA1 (ii) Maintain the bent elastic plate 11 and insert the cooling pipe 4 between the first end portion 11a and the central portion 11b. PA1 (iii) As shown in FIG. 6, insert the spacer 15 between the first end portion 11b and the central portion 11c. PA1 (iv) Screw on the screws 16 and combine the first end portion 11b and the central portion 11c. PA1 (i) Constant and high cooling capacity regardless of the position of the printed circuit board. PA1 (ii) Good heat conductivity in spite of irregular dimensions of component. PA1 (iii) A simplified construction process for the printed circuit board.
Because of the above complicated process for attaching the elastic plate 14, it is difficult to simplify the entire process for constructing the printed circuit board 1.